diff options
Diffstat (limited to 'mm/compaction.c')
| -rw-r--r-- | mm/compaction.c | 3068 |
1 files changed, 3068 insertions, 0 deletions
diff --git a/mm/compaction.c b/mm/compaction.c new file mode 100644 index 000000000..8238e8338 --- /dev/null +++ b/mm/compaction.c @@ -0,0 +1,3068 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * linux/mm/compaction.c + * + * Memory compaction for the reduction of external fragmentation. Note that + * this heavily depends upon page migration to do all the real heavy + * lifting + * + * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie> + */ +#include <linux/cpu.h> +#include <linux/swap.h> +#include <linux/migrate.h> +#include <linux/compaction.h> +#include <linux/mm_inline.h> +#include <linux/sched/signal.h> +#include <linux/backing-dev.h> +#include <linux/sysctl.h> +#include <linux/sysfs.h> +#include <linux/page-isolation.h> +#include <linux/kasan.h> +#include <linux/kthread.h> +#include <linux/freezer.h> +#include <linux/page_owner.h> +#include <linux/psi.h> +#include "internal.h" + +#ifdef CONFIG_COMPACTION +/* + * Fragmentation score check interval for proactive compaction purposes. + */ +#define HPAGE_FRAG_CHECK_INTERVAL_MSEC (500) + +static inline void count_compact_event(enum vm_event_item item) +{ + count_vm_event(item); +} + +static inline void count_compact_events(enum vm_event_item item, long delta) +{ + count_vm_events(item, delta); +} +#else +#define count_compact_event(item) do { } while (0) +#define count_compact_events(item, delta) do { } while (0) +#endif + +#if defined CONFIG_COMPACTION || defined CONFIG_CMA + +#define CREATE_TRACE_POINTS +#include <trace/events/compaction.h> + +#define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order)) +#define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order)) + +/* + * Page order with-respect-to which proactive compaction + * calculates external fragmentation, which is used as + * the "fragmentation score" of a node/zone. + */ +#if defined CONFIG_TRANSPARENT_HUGEPAGE +#define COMPACTION_HPAGE_ORDER HPAGE_PMD_ORDER +#elif defined CONFIG_HUGETLBFS +#define COMPACTION_HPAGE_ORDER HUGETLB_PAGE_ORDER +#else +#define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT) +#endif + +static unsigned long release_freepages(struct list_head *freelist) +{ + struct page *page, *next; + unsigned long high_pfn = 0; + + list_for_each_entry_safe(page, next, freelist, lru) { + unsigned long pfn = page_to_pfn(page); + list_del(&page->lru); + __free_page(page); + if (pfn > high_pfn) + high_pfn = pfn; + } + + return high_pfn; +} + +static void split_map_pages(struct list_head *list) +{ + unsigned int i, order, nr_pages; + struct page *page, *next; + LIST_HEAD(tmp_list); + + list_for_each_entry_safe(page, next, list, lru) { + list_del(&page->lru); + + order = page_private(page); + nr_pages = 1 << order; + + post_alloc_hook(page, order, __GFP_MOVABLE); + if (order) + split_page(page, order); + + for (i = 0; i < nr_pages; i++) { + list_add(&page->lru, &tmp_list); + page++; + } + } + + list_splice(&tmp_list, list); +} + +#ifdef CONFIG_COMPACTION +bool PageMovable(struct page *page) +{ + const struct movable_operations *mops; + + VM_BUG_ON_PAGE(!PageLocked(page), page); + if (!__PageMovable(page)) + return false; + + mops = page_movable_ops(page); + if (mops) + return true; + + return false; +} +EXPORT_SYMBOL(PageMovable); + +void __SetPageMovable(struct page *page, const struct movable_operations *mops) +{ + VM_BUG_ON_PAGE(!PageLocked(page), page); + VM_BUG_ON_PAGE((unsigned long)mops & PAGE_MAPPING_MOVABLE, page); + page->mapping = (void *)((unsigned long)mops | PAGE_MAPPING_MOVABLE); +} +EXPORT_SYMBOL(__SetPageMovable); + +void __ClearPageMovable(struct page *page) +{ + VM_BUG_ON_PAGE(!PageMovable(page), page); + /* + * This page still has the type of a movable page, but it's + * actually not movable any more. + */ + page->mapping = (void *)PAGE_MAPPING_MOVABLE; +} +EXPORT_SYMBOL(__ClearPageMovable); + +/* Do not skip compaction more than 64 times */ +#define COMPACT_MAX_DEFER_SHIFT 6 + +/* + * Compaction is deferred when compaction fails to result in a page + * allocation success. 1 << compact_defer_shift, compactions are skipped up + * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT + */ +static void defer_compaction(struct zone *zone, int order) +{ + zone->compact_considered = 0; + zone->compact_defer_shift++; + + if (order < zone->compact_order_failed) + zone->compact_order_failed = order; + + if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT) + zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT; + + trace_mm_compaction_defer_compaction(zone, order); +} + +/* Returns true if compaction should be skipped this time */ +static bool compaction_deferred(struct zone *zone, int order) +{ + unsigned long defer_limit = 1UL << zone->compact_defer_shift; + + if (order < zone->compact_order_failed) + return false; + + /* Avoid possible overflow */ + if (++zone->compact_considered >= defer_limit) { + zone->compact_considered = defer_limit; + return false; + } + + trace_mm_compaction_deferred(zone, order); + + return true; +} + +/* + * Update defer tracking counters after successful compaction of given order, + * which means an allocation either succeeded (alloc_success == true) or is + * expected to succeed. + */ +void compaction_defer_reset(struct zone *zone, int order, + bool alloc_success) +{ + if (alloc_success) { + zone->compact_considered = 0; + zone->compact_defer_shift = 0; + } + if (order >= zone->compact_order_failed) + zone->compact_order_failed = order + 1; + + trace_mm_compaction_defer_reset(zone, order); +} + +/* Returns true if restarting compaction after many failures */ +static bool compaction_restarting(struct zone *zone, int order) +{ + if (order < zone->compact_order_failed) + return false; + + return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT && + zone->compact_considered >= 1UL << zone->compact_defer_shift; +} + +/* Returns true if the pageblock should be scanned for pages to isolate. */ +static inline bool isolation_suitable(struct compact_control *cc, + struct page *page) +{ + if (cc->ignore_skip_hint) + return true; + + return !get_pageblock_skip(page); +} + +static void reset_cached_positions(struct zone *zone) +{ + zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn; + zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn; + zone->compact_cached_free_pfn = + pageblock_start_pfn(zone_end_pfn(zone) - 1); +} + +/* + * Compound pages of >= pageblock_order should consistently be skipped until + * released. It is always pointless to compact pages of such order (if they are + * migratable), and the pageblocks they occupy cannot contain any free pages. + */ +static bool pageblock_skip_persistent(struct page *page) +{ + if (!PageCompound(page)) + return false; + + page = compound_head(page); + + if (compound_order(page) >= pageblock_order) + return true; + + return false; +} + +static bool +__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source, + bool check_target) +{ + struct page *page = pfn_to_online_page(pfn); + struct page *block_page; + struct page *end_page; + unsigned long block_pfn; + + if (!page) + return false; + if (zone != page_zone(page)) + return false; + if (pageblock_skip_persistent(page)) + return false; + + /* + * If skip is already cleared do no further checking once the + * restart points have been set. + */ + if (check_source && check_target && !get_pageblock_skip(page)) + return true; + + /* + * If clearing skip for the target scanner, do not select a + * non-movable pageblock as the starting point. + */ + if (!check_source && check_target && + get_pageblock_migratetype(page) != MIGRATE_MOVABLE) + return false; + + /* Ensure the start of the pageblock or zone is online and valid */ + block_pfn = pageblock_start_pfn(pfn); + block_pfn = max(block_pfn, zone->zone_start_pfn); + block_page = pfn_to_online_page(block_pfn); + if (block_page) { + page = block_page; + pfn = block_pfn; + } + + /* Ensure the end of the pageblock or zone is online and valid */ + block_pfn = pageblock_end_pfn(pfn) - 1; + block_pfn = min(block_pfn, zone_end_pfn(zone) - 1); + end_page = pfn_to_online_page(block_pfn); + if (!end_page) + return false; + + /* + * Only clear the hint if a sample indicates there is either a + * free page or an LRU page in the block. One or other condition + * is necessary for the block to be a migration source/target. + */ + do { + if (check_source && PageLRU(page)) { + clear_pageblock_skip(page); + return true; + } + + if (check_target && PageBuddy(page)) { + clear_pageblock_skip(page); + return true; + } + + page += (1 << PAGE_ALLOC_COSTLY_ORDER); + } while (page <= end_page); + + return false; +} + +/* + * This function is called to clear all cached information on pageblocks that + * should be skipped for page isolation when the migrate and free page scanner + * meet. + */ +static void __reset_isolation_suitable(struct zone *zone) +{ + unsigned long migrate_pfn = zone->zone_start_pfn; + unsigned long free_pfn = zone_end_pfn(zone) - 1; + unsigned long reset_migrate = free_pfn; + unsigned long reset_free = migrate_pfn; + bool source_set = false; + bool free_set = false; + + if (!zone->compact_blockskip_flush) + return; + + zone->compact_blockskip_flush = false; + + /* + * Walk the zone and update pageblock skip information. Source looks + * for PageLRU while target looks for PageBuddy. When the scanner + * is found, both PageBuddy and PageLRU are checked as the pageblock + * is suitable as both source and target. + */ + for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages, + free_pfn -= pageblock_nr_pages) { + cond_resched(); + + /* Update the migrate PFN */ + if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) && + migrate_pfn < reset_migrate) { + source_set = true; + reset_migrate = migrate_pfn; + zone->compact_init_migrate_pfn = reset_migrate; + zone->compact_cached_migrate_pfn[0] = reset_migrate; + zone->compact_cached_migrate_pfn[1] = reset_migrate; + } + + /* Update the free PFN */ + if (__reset_isolation_pfn(zone, free_pfn, free_set, true) && + free_pfn > reset_free) { + free_set = true; + reset_free = free_pfn; + zone->compact_init_free_pfn = reset_free; + zone->compact_cached_free_pfn = reset_free; + } + } + + /* Leave no distance if no suitable block was reset */ + if (reset_migrate >= reset_free) { + zone->compact_cached_migrate_pfn[0] = migrate_pfn; + zone->compact_cached_migrate_pfn[1] = migrate_pfn; + zone->compact_cached_free_pfn = free_pfn; + } +} + +void reset_isolation_suitable(pg_data_t *pgdat) +{ + int zoneid; + + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { + struct zone *zone = &pgdat->node_zones[zoneid]; + if (!populated_zone(zone)) + continue; + + /* Only flush if a full compaction finished recently */ + if (zone->compact_blockskip_flush) + __reset_isolation_suitable(zone); + } +} + +/* + * Sets the pageblock skip bit if it was clear. Note that this is a hint as + * locks are not required for read/writers. Returns true if it was already set. + */ +static bool test_and_set_skip(struct compact_control *cc, struct page *page, + unsigned long pfn) +{ + bool skip; + + /* Do no update if skip hint is being ignored */ + if (cc->ignore_skip_hint) + return false; + + if (!pageblock_aligned(pfn)) + return false; + + skip = get_pageblock_skip(page); + if (!skip && !cc->no_set_skip_hint) + set_pageblock_skip(page); + + return skip; +} + +static void update_cached_migrate(struct compact_control *cc, unsigned long pfn) +{ + struct zone *zone = cc->zone; + + pfn = pageblock_end_pfn(pfn); + + /* Set for isolation rather than compaction */ + if (cc->no_set_skip_hint) + return; + + if (pfn > zone->compact_cached_migrate_pfn[0]) + zone->compact_cached_migrate_pfn[0] = pfn; + if (cc->mode != MIGRATE_ASYNC && + pfn > zone->compact_cached_migrate_pfn[1]) + zone->compact_cached_migrate_pfn[1] = pfn; +} + +/* + * If no pages were isolated then mark this pageblock to be skipped in the + * future. The information is later cleared by __reset_isolation_suitable(). + */ +static void update_pageblock_skip(struct compact_control *cc, + struct page *page, unsigned long pfn) +{ + struct zone *zone = cc->zone; + + if (cc->no_set_skip_hint) + return; + + if (!page) + return; + + set_pageblock_skip(page); + + /* Update where async and sync compaction should restart */ + if (pfn < zone->compact_cached_free_pfn) + zone->compact_cached_free_pfn = pfn; +} +#else +static inline bool isolation_suitable(struct compact_control *cc, + struct page *page) +{ + return true; +} + +static inline bool pageblock_skip_persistent(struct page *page) +{ + return false; +} + +static inline void update_pageblock_skip(struct compact_control *cc, + struct page *page, unsigned long pfn) +{ +} + +static void update_cached_migrate(struct compact_control *cc, unsigned long pfn) +{ +} + +static bool test_and_set_skip(struct compact_control *cc, struct page *page, + unsigned long pfn) +{ + return false; +} +#endif /* CONFIG_COMPACTION */ + +/* + * Compaction requires the taking of some coarse locks that are potentially + * very heavily contended. For async compaction, trylock and record if the + * lock is contended. The lock will still be acquired but compaction will + * abort when the current block is finished regardless of success rate. + * Sync compaction acquires the lock. + * + * Always returns true which makes it easier to track lock state in callers. + */ +static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags, + struct compact_control *cc) + __acquires(lock) +{ + /* Track if the lock is contended in async mode */ + if (cc->mode == MIGRATE_ASYNC && !cc->contended) { + if (spin_trylock_irqsave(lock, *flags)) + return true; + + cc->contended = true; + } + + spin_lock_irqsave(lock, *flags); + return true; +} + +/* + * Compaction requires the taking of some coarse locks that are potentially + * very heavily contended. The lock should be periodically unlocked to avoid + * having disabled IRQs for a long time, even when there is nobody waiting on + * the lock. It might also be that allowing the IRQs will result in + * need_resched() becoming true. If scheduling is needed, compaction schedules. + * Either compaction type will also abort if a fatal signal is pending. + * In either case if the lock was locked, it is dropped and not regained. + * + * Returns true if compaction should abort due to fatal signal pending. + * Returns false when compaction can continue. + */ +static bool compact_unlock_should_abort(spinlock_t *lock, + unsigned long flags, bool *locked, struct compact_control *cc) +{ + if (*locked) { + spin_unlock_irqrestore(lock, flags); + *locked = false; + } + + if (fatal_signal_pending(current)) { + cc->contended = true; + return true; + } + + cond_resched(); + + return false; +} + +/* + * Isolate free pages onto a private freelist. If @strict is true, will abort + * returning 0 on any invalid PFNs or non-free pages inside of the pageblock + * (even though it may still end up isolating some pages). + */ +static unsigned long isolate_freepages_block(struct compact_control *cc, + unsigned long *start_pfn, + unsigned long end_pfn, + struct list_head *freelist, + unsigned int stride, + bool strict) +{ + int nr_scanned = 0, total_isolated = 0; + struct page *cursor; + unsigned long flags = 0; + bool locked = false; + unsigned long blockpfn = *start_pfn; + unsigned int order; + + /* Strict mode is for isolation, speed is secondary */ + if (strict) + stride = 1; + + cursor = pfn_to_page(blockpfn); + + /* Isolate free pages. */ + for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) { + int isolated; + struct page *page = cursor; + + /* + * Periodically drop the lock (if held) regardless of its + * contention, to give chance to IRQs. Abort if fatal signal + * pending. + */ + if (!(blockpfn % COMPACT_CLUSTER_MAX) + && compact_unlock_should_abort(&cc->zone->lock, flags, + &locked, cc)) + break; + + nr_scanned++; + + /* + * For compound pages such as THP and hugetlbfs, we can save + * potentially a lot of iterations if we skip them at once. + * The check is racy, but we can consider only valid values + * and the only danger is skipping too much. + */ + if (PageCompound(page)) { + const unsigned int order = compound_order(page); + + if (likely(order < MAX_ORDER)) { + blockpfn += (1UL << order) - 1; + cursor += (1UL << order) - 1; + } + goto isolate_fail; + } + + if (!PageBuddy(page)) + goto isolate_fail; + + /* If we already hold the lock, we can skip some rechecking. */ + if (!locked) { + locked = compact_lock_irqsave(&cc->zone->lock, + &flags, cc); + + /* Recheck this is a buddy page under lock */ + if (!PageBuddy(page)) + goto isolate_fail; + } + + /* Found a free page, will break it into order-0 pages */ + order = buddy_order(page); + isolated = __isolate_free_page(page, order); + if (!isolated) + break; + set_page_private(page, order); + + nr_scanned += isolated - 1; + total_isolated += isolated; + cc->nr_freepages += isolated; + list_add_tail(&page->lru, freelist); + + if (!strict && cc->nr_migratepages <= cc->nr_freepages) { + blockpfn += isolated; + break; + } + /* Advance to the end of split page */ + blockpfn += isolated - 1; + cursor += isolated - 1; + continue; + +isolate_fail: + if (strict) + break; + else + continue; + + } + + if (locked) + spin_unlock_irqrestore(&cc->zone->lock, flags); + + /* + * There is a tiny chance that we have read bogus compound_order(), + * so be careful to not go outside of the pageblock. + */ + if (unlikely(blockpfn > end_pfn)) + blockpfn = end_pfn; + + trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn, + nr_scanned, total_isolated); + + /* Record how far we have got within the block */ + *start_pfn = blockpfn; + + /* + * If strict isolation is requested by CMA then check that all the + * pages requested were isolated. If there were any failures, 0 is + * returned and CMA will fail. + */ + if (strict && blockpfn < end_pfn) + total_isolated = 0; + + cc->total_free_scanned += nr_scanned; + if (total_isolated) + count_compact_events(COMPACTISOLATED, total_isolated); + return total_isolated; +} + +/** + * isolate_freepages_range() - isolate free pages. + * @cc: Compaction control structure. + * @start_pfn: The first PFN to start isolating. + * @end_pfn: The one-past-last PFN. + * + * Non-free pages, invalid PFNs, or zone boundaries within the + * [start_pfn, end_pfn) range are considered errors, cause function to + * undo its actions and return zero. + * + * Otherwise, function returns one-past-the-last PFN of isolated page + * (which may be greater then end_pfn if end fell in a middle of + * a free page). + */ +unsigned long +isolate_freepages_range(struct compact_control *cc, + unsigned long start_pfn, unsigned long end_pfn) +{ + unsigned long isolated, pfn, block_start_pfn, block_end_pfn; + LIST_HEAD(freelist); + + pfn = start_pfn; + block_start_pfn = pageblock_start_pfn(pfn); + if (block_start_pfn < cc->zone->zone_start_pfn) + block_start_pfn = cc->zone->zone_start_pfn; + block_end_pfn = pageblock_end_pfn(pfn); + + for (; pfn < end_pfn; pfn += isolated, + block_start_pfn = block_end_pfn, + block_end_pfn += pageblock_nr_pages) { + /* Protect pfn from changing by isolate_freepages_block */ + unsigned long isolate_start_pfn = pfn; + + block_end_pfn = min(block_end_pfn, end_pfn); + + /* + * pfn could pass the block_end_pfn if isolated freepage + * is more than pageblock order. In this case, we adjust + * scanning range to right one. + */ + if (pfn >= block_end_pfn) { + block_start_pfn = pageblock_start_pfn(pfn); + block_end_pfn = pageblock_end_pfn(pfn); + block_end_pfn = min(block_end_pfn, end_pfn); + } + + if (!pageblock_pfn_to_page(block_start_pfn, + block_end_pfn, cc->zone)) + break; + + isolated = isolate_freepages_block(cc, &isolate_start_pfn, + block_end_pfn, &freelist, 0, true); + + /* + * In strict mode, isolate_freepages_block() returns 0 if + * there are any holes in the block (ie. invalid PFNs or + * non-free pages). + */ + if (!isolated) + break; + + /* + * If we managed to isolate pages, it is always (1 << n) * + * pageblock_nr_pages for some non-negative n. (Max order + * page may span two pageblocks). + */ + } + + /* __isolate_free_page() does not map the pages */ + split_map_pages(&freelist); + + if (pfn < end_pfn) { + /* Loop terminated early, cleanup. */ + release_freepages(&freelist); + return 0; + } + + /* We don't use freelists for anything. */ + return pfn; +} + +/* Similar to reclaim, but different enough that they don't share logic */ +static bool too_many_isolated(pg_data_t *pgdat) +{ + bool too_many; + + unsigned long active, inactive, isolated; + + inactive = node_page_state(pgdat, NR_INACTIVE_FILE) + + node_page_state(pgdat, NR_INACTIVE_ANON); + active = node_page_state(pgdat, NR_ACTIVE_FILE) + + node_page_state(pgdat, NR_ACTIVE_ANON); + isolated = node_page_state(pgdat, NR_ISOLATED_FILE) + + node_page_state(pgdat, NR_ISOLATED_ANON); + + too_many = isolated > (inactive + active) / 2; + if (!too_many) + wake_throttle_isolated(pgdat); + + return too_many; +} + +/** + * isolate_migratepages_block() - isolate all migrate-able pages within + * a single pageblock + * @cc: Compaction control structure. + * @low_pfn: The first PFN to isolate + * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock + * @mode: Isolation mode to be used. + * + * Isolate all pages that can be migrated from the range specified by + * [low_pfn, end_pfn). The range is expected to be within same pageblock. + * Returns errno, like -EAGAIN or -EINTR in case e.g signal pending or congestion, + * -ENOMEM in case we could not allocate a page, or 0. + * cc->migrate_pfn will contain the next pfn to scan. + * + * The pages are isolated on cc->migratepages list (not required to be empty), + * and cc->nr_migratepages is updated accordingly. + */ +static int +isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, + unsigned long end_pfn, isolate_mode_t mode) +{ + pg_data_t *pgdat = cc->zone->zone_pgdat; + unsigned long nr_scanned = 0, nr_isolated = 0; + struct lruvec *lruvec; + unsigned long flags = 0; + struct lruvec *locked = NULL; + struct page *page = NULL, *valid_page = NULL; + struct address_space *mapping; + unsigned long start_pfn = low_pfn; + bool skip_on_failure = false; + unsigned long next_skip_pfn = 0; + bool skip_updated = false; + int ret = 0; + + cc->migrate_pfn = low_pfn; + + /* + * Ensure that there are not too many pages isolated from the LRU + * list by either parallel reclaimers or compaction. If there are, + * delay for some time until fewer pages are isolated + */ + while (unlikely(too_many_isolated(pgdat))) { + /* stop isolation if there are still pages not migrated */ + if (cc->nr_migratepages) + return -EAGAIN; + + /* async migration should just abort */ + if (cc->mode == MIGRATE_ASYNC) + return -EAGAIN; + + reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED); + + if (fatal_signal_pending(current)) + return -EINTR; + } + + cond_resched(); + + if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) { + skip_on_failure = true; + next_skip_pfn = block_end_pfn(low_pfn, cc->order); + } + + /* Time to isolate some pages for migration */ + for (; low_pfn < end_pfn; low_pfn++) { + + if (skip_on_failure && low_pfn >= next_skip_pfn) { + /* + * We have isolated all migration candidates in the + * previous order-aligned block, and did not skip it due + * to failure. We should migrate the pages now and + * hopefully succeed compaction. + */ + if (nr_isolated) + break; + + /* + * We failed to isolate in the previous order-aligned + * block. Set the new boundary to the end of the + * current block. Note we can't simply increase + * next_skip_pfn by 1 << order, as low_pfn might have + * been incremented by a higher number due to skipping + * a compound or a high-order buddy page in the + * previous loop iteration. + */ + next_skip_pfn = block_end_pfn(low_pfn, cc->order); + } + + /* + * Periodically drop the lock (if held) regardless of its + * contention, to give chance to IRQs. Abort completely if + * a fatal signal is pending. + */ + if (!(low_pfn % COMPACT_CLUSTER_MAX)) { + if (locked) { + unlock_page_lruvec_irqrestore(locked, flags); + locked = NULL; + } + + if (fatal_signal_pending(current)) { + cc->contended = true; + ret = -EINTR; + + goto fatal_pending; + } + + cond_resched(); + } + + nr_scanned++; + + page = pfn_to_page(low_pfn); + + /* + * Check if the pageblock has already been marked skipped. + * Only the aligned PFN is checked as the caller isolates + * COMPACT_CLUSTER_MAX at a time so the second call must + * not falsely conclude that the block should be skipped. + */ + if (!valid_page && pageblock_aligned(low_pfn)) { + if (!isolation_suitable(cc, page)) { + low_pfn = end_pfn; + page = NULL; + goto isolate_abort; + } + valid_page = page; + } + + if (PageHuge(page) && cc->alloc_contig) { + ret = isolate_or_dissolve_huge_page(page, &cc->migratepages); + + /* + * Fail isolation in case isolate_or_dissolve_huge_page() + * reports an error. In case of -ENOMEM, abort right away. + */ + if (ret < 0) { + /* Do not report -EBUSY down the chain */ + if (ret == -EBUSY) + ret = 0; + low_pfn += compound_nr(page) - 1; + goto isolate_fail; + } + + if (PageHuge(page)) { + /* + * Hugepage was successfully isolated and placed + * on the cc->migratepages list. + */ + low_pfn += compound_nr(page) - 1; + goto isolate_success_no_list; + } + + /* + * Ok, the hugepage was dissolved. Now these pages are + * Buddy and cannot be re-allocated because they are + * isolated. Fall-through as the check below handles + * Buddy pages. + */ + } + + /* + * Skip if free. We read page order here without zone lock + * which is generally unsafe, but the race window is small and + * the worst thing that can happen is that we skip some + * potential isolation targets. + */ + if (PageBuddy(page)) { + unsigned long freepage_order = buddy_order_unsafe(page); + + /* + * Without lock, we cannot be sure that what we got is + * a valid page order. Consider only values in the + * valid order range to prevent low_pfn overflow. + */ + if (freepage_order > 0 && freepage_order < MAX_ORDER) + low_pfn += (1UL << freepage_order) - 1; + continue; + } + + /* + * Regardless of being on LRU, compound pages such as THP and + * hugetlbfs are not to be compacted unless we are attempting + * an allocation much larger than the huge page size (eg CMA). + * We can potentially save a lot of iterations if we skip them + * at once. The check is racy, but we can consider only valid + * values and the only danger is skipping too much. + */ + if (PageCompound(page) && !cc->alloc_contig) { + const unsigned int order = compound_order(page); + + if (likely(order < MAX_ORDER)) + low_pfn += (1UL << order) - 1; + goto isolate_fail; + } + + /* + * Check may be lockless but that's ok as we recheck later. + * It's possible to migrate LRU and non-lru movable pages. + * Skip any other type of page + */ + if (!PageLRU(page)) { + /* + * __PageMovable can return false positive so we need + * to verify it under page_lock. + */ + if (unlikely(__PageMovable(page)) && + !PageIsolated(page)) { + if (locked) { + unlock_page_lruvec_irqrestore(locked, flags); + locked = NULL; + } + + if (!isolate_movable_page(page, mode)) + goto isolate_success; + } + + goto isolate_fail; + } + + /* + * Be careful not to clear PageLRU until after we're + * sure the page is not being freed elsewhere -- the + * page release code relies on it. + */ + if (unlikely(!get_page_unless_zero(page))) + goto isolate_fail; + + /* + * Migration will fail if an anonymous page is pinned in memory, + * so avoid taking lru_lock and isolating it unnecessarily in an + * admittedly racy check. + */ + mapping = page_mapping(page); + if (!mapping && (page_count(page) - 1) > total_mapcount(page)) + goto isolate_fail_put; + + /* + * Only allow to migrate anonymous pages in GFP_NOFS context + * because those do not depend on fs locks. + */ + if (!(cc->gfp_mask & __GFP_FS) && mapping) + goto isolate_fail_put; + + /* Only take pages on LRU: a check now makes later tests safe */ + if (!PageLRU(page)) + goto isolate_fail_put; + + /* Compaction might skip unevictable pages but CMA takes them */ + if (!(mode & ISOLATE_UNEVICTABLE) && PageUnevictable(page)) + goto isolate_fail_put; + + /* + * To minimise LRU disruption, the caller can indicate with + * ISOLATE_ASYNC_MIGRATE that it only wants to isolate pages + * it will be able to migrate without blocking - clean pages + * for the most part. PageWriteback would require blocking. + */ + if ((mode & ISOLATE_ASYNC_MIGRATE) && PageWriteback(page)) + goto isolate_fail_put; + + if ((mode & ISOLATE_ASYNC_MIGRATE) && PageDirty(page)) { + bool migrate_dirty; + + /* + * Only pages without mappings or that have a + * ->migrate_folio callback are possible to migrate + * without blocking. However, we can be racing with + * truncation so it's necessary to lock the page + * to stabilise the mapping as truncation holds + * the page lock until after the page is removed + * from the page cache. + */ + if (!trylock_page(page)) + goto isolate_fail_put; + + mapping = page_mapping(page); + migrate_dirty = !mapping || + mapping->a_ops->migrate_folio; + unlock_page(page); + if (!migrate_dirty) + goto isolate_fail_put; + } + + /* Try isolate the page */ + if (!TestClearPageLRU(page)) + goto isolate_fail_put; + + lruvec = folio_lruvec(page_folio(page)); + + /* If we already hold the lock, we can skip some rechecking */ + if (lruvec != locked) { + if (locked) + unlock_page_lruvec_irqrestore(locked, flags); + + compact_lock_irqsave(&lruvec->lru_lock, &flags, cc); + locked = lruvec; + + lruvec_memcg_debug(lruvec, page_folio(page)); + + /* Try get exclusive access under lock */ + if (!skip_updated) { + skip_updated = true; + if (test_and_set_skip(cc, page, low_pfn)) + goto isolate_abort; + } + + /* + * Page become compound since the non-locked check, + * and it's on LRU. It can only be a THP so the order + * is safe to read and it's 0 for tail pages. + */ + if (unlikely(PageCompound(page) && !cc->alloc_contig)) { + low_pfn += compound_nr(page) - 1; + SetPageLRU(page); + goto isolate_fail_put; + } + } + + /* The whole page is taken off the LRU; skip the tail pages. */ + if (PageCompound(page)) + low_pfn += compound_nr(page) - 1; + + /* Successfully isolated */ + del_page_from_lru_list(page, lruvec); + mod_node_page_state(page_pgdat(page), + NR_ISOLATED_ANON + page_is_file_lru(page), + thp_nr_pages(page)); + +isolate_success: + list_add(&page->lru, &cc->migratepages); +isolate_success_no_list: + cc->nr_migratepages += compound_nr(page); + nr_isolated += compound_nr(page); + nr_scanned += compound_nr(page) - 1; + + /* + * Avoid isolating too much unless this block is being + * rescanned (e.g. dirty/writeback pages, parallel allocation) + * or a lock is contended. For contention, isolate quickly to + * potentially remove one source of contention. + */ + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX && + !cc->rescan && !cc->contended) { + ++low_pfn; + break; + } + + continue; + +isolate_fail_put: + /* Avoid potential deadlock in freeing page under lru_lock */ + if (locked) { + unlock_page_lruvec_irqrestore(locked, flags); + locked = NULL; + } + put_page(page); + +isolate_fail: + if (!skip_on_failure && ret != -ENOMEM) + continue; + + /* + * We have isolated some pages, but then failed. Release them + * instead of migrating, as we cannot form the cc->order buddy + * page anyway. + */ + if (nr_isolated) { + if (locked) { + unlock_page_lruvec_irqrestore(locked, flags); + locked = NULL; + } + putback_movable_pages(&cc->migratepages); + cc->nr_migratepages = 0; + nr_isolated = 0; + } + + if (low_pfn < next_skip_pfn) { + low_pfn = next_skip_pfn - 1; + /* + * The check near the loop beginning would have updated + * next_skip_pfn too, but this is a bit simpler. + */ + next_skip_pfn += 1UL << cc->order; + } + + if (ret == -ENOMEM) + break; + } + + /* + * The PageBuddy() check could have potentially brought us outside + * the range to be scanned. + */ + if (unlikely(low_pfn > end_pfn)) + low_pfn = end_pfn; + + page = NULL; + +isolate_abort: + if (locked) + unlock_page_lruvec_irqrestore(locked, flags); + if (page) { + SetPageLRU(page); + put_page(page); + } + + /* + * Updated the cached scanner pfn once the pageblock has been scanned + * Pages will either be migrated in which case there is no point + * scanning in the near future or migration failed in which case the + * failure reason may persist. The block is marked for skipping if + * there were no pages isolated in the block or if the block is + * rescanned twice in a row. + */ + if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) { + if (valid_page && !skip_updated) + set_pageblock_skip(valid_page); + update_cached_migrate(cc, low_pfn); + } + + trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn, + nr_scanned, nr_isolated); + +fatal_pending: + cc->total_migrate_scanned += nr_scanned; + if (nr_isolated) + count_compact_events(COMPACTISOLATED, nr_isolated); + + cc->migrate_pfn = low_pfn; + + return ret; +} + +/** + * isolate_migratepages_range() - isolate migrate-able pages in a PFN range + * @cc: Compaction control structure. + * @start_pfn: The first PFN to start isolating. + * @end_pfn: The one-past-last PFN. + * + * Returns -EAGAIN when contented, -EINTR in case of a signal pending, -ENOMEM + * in case we could not allocate a page, or 0. + */ +int +isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn, + unsigned long end_pfn) +{ + unsigned long pfn, block_start_pfn, block_end_pfn; + int ret = 0; + + /* Scan block by block. First and last block may be incomplete */ + pfn = start_pfn; + block_start_pfn = pageblock_start_pfn(pfn); + if (block_start_pfn < cc->zone->zone_start_pfn) + block_start_pfn = cc->zone->zone_start_pfn; + block_end_pfn = pageblock_end_pfn(pfn); + + for (; pfn < end_pfn; pfn = block_end_pfn, + block_start_pfn = block_end_pfn, + block_end_pfn += pageblock_nr_pages) { + + block_end_pfn = min(block_end_pfn, end_pfn); + + if (!pageblock_pfn_to_page(block_start_pfn, + block_end_pfn, cc->zone)) + continue; + + ret = isolate_migratepages_block(cc, pfn, block_end_pfn, + ISOLATE_UNEVICTABLE); + + if (ret) + break; + + if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX) + break; + } + + return ret; +} + +#endif /* CONFIG_COMPACTION || CONFIG_CMA */ +#ifdef CONFIG_COMPACTION + +static bool suitable_migration_source(struct compact_control *cc, + struct page *page) +{ + int block_mt; + + if (pageblock_skip_persistent(page)) + return false; + + if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction) + return true; + + block_mt = get_pageblock_migratetype(page); + + if (cc->migratetype == MIGRATE_MOVABLE) + return is_migrate_movable(block_mt); + else + return block_mt == cc->migratetype; +} + +/* Returns true if the page is within a block suitable for migration to */ +static bool suitable_migration_target(struct compact_control *cc, + struct page *page) +{ + /* If the page is a large free page, then disallow migration */ + if (PageBuddy(page)) { + /* + * We are checking page_order without zone->lock taken. But + * the only small danger is that we skip a potentially suitable + * pageblock, so it's not worth to check order for valid range. + */ + if (buddy_order_unsafe(page) >= pageblock_order) + return false; + } + + if (cc->ignore_block_suitable) + return true; + + /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */ + if (is_migrate_movable(get_pageblock_migratetype(page))) + return true; + + /* Otherwise skip the block */ + return false; +} + +static inline unsigned int +freelist_scan_limit(struct compact_control *cc) +{ + unsigned short shift = BITS_PER_LONG - 1; + + return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1; +} + +/* + * Test whether the free scanner has reached the same or lower pageblock than + * the migration scanner, and compaction should thus terminate. + */ +static inline bool compact_scanners_met(struct compact_control *cc) +{ + return (cc->free_pfn >> pageblock_order) + <= (cc->migrate_pfn >> pageblock_order); +} + +/* + * Used when scanning for a suitable migration target which scans freelists + * in reverse. Reorders the list such as the unscanned pages are scanned + * first on the next iteration of the free scanner + */ +static void +move_freelist_head(struct list_head *freelist, struct page *freepage) +{ + LIST_HEAD(sublist); + + if (!list_is_last(freelist, &freepage->lru)) { + list_cut_before(&sublist, freelist, &freepage->lru); + list_splice_tail(&sublist, freelist); + } +} + +/* + * Similar to move_freelist_head except used by the migration scanner + * when scanning forward. It's possible for these list operations to + * move against each other if they search the free list exactly in + * lockstep. + */ +static void +move_freelist_tail(struct list_head *freelist, struct page *freepage) +{ + LIST_HEAD(sublist); + + if (!list_is_first(freelist, &freepage->lru)) { + list_cut_position(&sublist, freelist, &freepage->lru); + list_splice_tail(&sublist, freelist); + } +} + +static void +fast_isolate_around(struct compact_control *cc, unsigned long pfn) +{ + unsigned long start_pfn, end_pfn; + struct page *page; + + /* Do not search around if there are enough pages already */ + if (cc->nr_freepages >= cc->nr_migratepages) + return; + + /* Minimise scanning during async compaction */ + if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC) + return; + + /* Pageblock boundaries */ + start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn); + end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)); + + page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone); + if (!page) + return; + + isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false); + + /* Skip this pageblock in the future as it's full or nearly full */ + if (cc->nr_freepages < cc->nr_migratepages) + set_pageblock_skip(page); + + return; +} + +/* Search orders in round-robin fashion */ +static int next_search_order(struct compact_control *cc, int order) +{ + order--; + if (order < 0) + order = cc->order - 1; + + /* Search wrapped around? */ + if (order == cc->search_order) { + cc->search_order--; + if (cc->search_order < 0) + cc->search_order = cc->order - 1; + return -1; + } + + return order; +} + +static unsigned long +fast_isolate_freepages(struct compact_control *cc) +{ + unsigned int limit = max(1U, freelist_scan_limit(cc) >> 1); + unsigned int nr_scanned = 0; + unsigned long low_pfn, min_pfn, highest = 0; + unsigned long nr_isolated = 0; + unsigned long distance; + struct page *page = NULL; + bool scan_start = false; + int order; + + /* Full compaction passes in a negative order */ + if (cc->order <= 0) + return cc->free_pfn; + + /* + * If starting the scan, use a deeper search and use the highest + * PFN found if a suitable one is not found. + */ + if (cc->free_pfn >= cc->zone->compact_init_free_pfn) { + limit = pageblock_nr_pages >> 1; + scan_start = true; + } + + /* + * Preferred point is in the top quarter of the scan space but take + * a pfn from the top half if the search is problematic. + */ + distance = (cc->free_pfn - cc->migrate_pfn); + low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2)); + min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1)); + + if (WARN_ON_ONCE(min_pfn > low_pfn)) + low_pfn = min_pfn; + + /* + * Search starts from the last successful isolation order or the next + * order to search after a previous failure + */ + cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order); + + for (order = cc->search_order; + !page && order >= 0; + order = next_search_order(cc, order)) { + struct free_area *area = &cc->zone->free_area[order]; + struct list_head *freelist; + struct page *freepage; + unsigned long flags; + unsigned int order_scanned = 0; + unsigned long high_pfn = 0; + + if (!area->nr_free) + continue; + + spin_lock_irqsave(&cc->zone->lock, flags); + freelist = &area->free_list[MIGRATE_MOVABLE]; + list_for_each_entry_reverse(freepage, freelist, lru) { + unsigned long pfn; + + order_scanned++; + nr_scanned++; + pfn = page_to_pfn(freepage); + + if (pfn >= highest) + highest = max(pageblock_start_pfn(pfn), + cc->zone->zone_start_pfn); + + if (pfn >= low_pfn) { + cc->fast_search_fail = 0; + cc->search_order = order; + page = freepage; + break; + } + + if (pfn >= min_pfn && pfn > high_pfn) { + high_pfn = pfn; + + /* Shorten the scan if a candidate is found */ + limit >>= 1; + } + + if (order_scanned >= limit) + break; + } + + /* Use a minimum pfn if a preferred one was not found */ + if (!page && high_pfn) { + page = pfn_to_page(high_pfn); + + /* Update freepage for the list reorder below */ + freepage = page; + } + + /* Reorder to so a future search skips recent pages */ + move_freelist_head(freelist, freepage); + + /* Isolate the page if available */ + if (page) { + if (__isolate_free_page(page, order)) { + set_page_private(page, order); + nr_isolated = 1 << order; + nr_scanned += nr_isolated - 1; + cc->nr_freepages += nr_isolated; + list_add_tail(&page->lru, &cc->freepages); + count_compact_events(COMPACTISOLATED, nr_isolated); + } else { + /* If isolation fails, abort the search */ + order = cc->search_order + 1; + page = NULL; + } + } + + spin_unlock_irqrestore(&cc->zone->lock, flags); + + /* + * Smaller scan on next order so the total scan is related + * to freelist_scan_limit. + */ + if (order_scanned >= limit) + limit = max(1U, limit >> 1); + } + + if (!page) { + cc->fast_search_fail++; + if (scan_start) { + /* + * Use the highest PFN found above min. If one was + * not found, be pessimistic for direct compaction + * and use the min mark. + */ + if (highest >= min_pfn) { + page = pfn_to_page(highest); + cc->free_pfn = highest; + } else { + if (cc->direct_compaction && pfn_valid(min_pfn)) { + page = pageblock_pfn_to_page(min_pfn, + min(pageblock_end_pfn(min_pfn), + zone_end_pfn(cc->zone)), + cc->zone); + cc->free_pfn = min_pfn; + } + } + } + } + + if (highest && highest >= cc->zone->compact_cached_free_pfn) { + highest -= pageblock_nr_pages; + cc->zone->compact_cached_free_pfn = highest; + } + + cc->total_free_scanned += nr_scanned; + if (!page) + return cc->free_pfn; + + low_pfn = page_to_pfn(page); + fast_isolate_around(cc, low_pfn); + return low_pfn; +} + +/* + * Based on information in the current compact_control, find blocks + * suitable for isolating free pages from and then isolate them. + */ +static void isolate_freepages(struct compact_control *cc) +{ + struct zone *zone = cc->zone; + struct page *page; + unsigned long block_start_pfn; /* start of current pageblock */ + unsigned long isolate_start_pfn; /* exact pfn we start at */ + unsigned long block_end_pfn; /* end of current pageblock */ + unsigned long low_pfn; /* lowest pfn scanner is able to scan */ + struct list_head *freelist = &cc->freepages; + unsigned int stride; + + /* Try a small search of the free lists for a candidate */ + fast_isolate_freepages(cc); + if (cc->nr_freepages) + goto splitmap; + + /* + * Initialise the free scanner. The starting point is where we last + * successfully isolated from, zone-cached value, or the end of the + * zone when isolating for the first time. For looping we also need + * this pfn aligned down to the pageblock boundary, because we do + * block_start_pfn -= pageblock_nr_pages in the for loop. + * For ending point, take care when isolating in last pageblock of a + * zone which ends in the middle of a pageblock. + * The low boundary is the end of the pageblock the migration scanner + * is using. + */ + isolate_start_pfn = cc->free_pfn; + block_start_pfn = pageblock_start_pfn(isolate_start_pfn); + block_end_pfn = min(block_start_pfn + pageblock_nr_pages, + zone_end_pfn(zone)); + low_pfn = pageblock_end_pfn(cc->migrate_pfn); + stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1; + + /* + * Isolate free pages until enough are available to migrate the + * pages on cc->migratepages. We stop searching if the migrate + * and free page scanners meet or enough free pages are isolated. + */ + for (; block_start_pfn >= low_pfn; + block_end_pfn = block_start_pfn, + block_start_pfn -= pageblock_nr_pages, + isolate_start_pfn = block_start_pfn) { + unsigned long nr_isolated; + + /* + * This can iterate a massively long zone without finding any + * suitable migration targets, so periodically check resched. + */ + if (!(block_start_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages))) + cond_resched(); + + page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn, + zone); + if (!page) + continue; + + /* Check the block is suitable for migration */ + if (!suitable_migration_target(cc, page)) + continue; + + /* If isolation recently failed, do not retry */ + if (!isolation_suitable(cc, page)) + continue; + + /* Found a block suitable for isolating free pages from. */ + nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn, + block_end_pfn, freelist, stride, false); + + /* Update the skip hint if the full pageblock was scanned */ + if (isolate_start_pfn == block_end_pfn) + update_pageblock_skip(cc, page, block_start_pfn); + + /* Are enough freepages isolated? */ + if (cc->nr_freepages >= cc->nr_migratepages) { + if (isolate_start_pfn >= block_end_pfn) { + /* + * Restart at previous pageblock if more + * freepages can be isolated next time. + */ + isolate_start_pfn = + block_start_pfn - pageblock_nr_pages; + } + break; + } else if (isolate_start_pfn < block_end_pfn) { + /* + * If isolation failed early, do not continue + * needlessly. + */ + break; + } + + /* Adjust stride depending on isolation */ + if (nr_isolated) { + stride = 1; + continue; + } + stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1); + } + + /* + * Record where the free scanner will restart next time. Either we + * broke from the loop and set isolate_start_pfn based on the last + * call to isolate_freepages_block(), or we met the migration scanner + * and the loop terminated due to isolate_start_pfn < low_pfn + */ + cc->free_pfn = isolate_start_pfn; + +splitmap: + /* __isolate_free_page() does not map the pages */ + split_map_pages(freelist); +} + +/* + * This is a migrate-callback that "allocates" freepages by taking pages + * from the isolated freelists in the block we are migrating to. + */ +static struct page *compaction_alloc(struct page *migratepage, + unsigned long data) +{ + struct compact_control *cc = (struct compact_control *)data; + struct page *freepage; + + if (list_empty(&cc->freepages)) { + isolate_freepages(cc); + + if (list_empty(&cc->freepages)) + return NULL; + } + + freepage = list_entry(cc->freepages.next, struct page, lru); + list_del(&freepage->lru); + cc->nr_freepages--; + + return freepage; +} + +/* + * This is a migrate-callback that "frees" freepages back to the isolated + * freelist. All pages on the freelist are from the same zone, so there is no + * special handling needed for NUMA. + */ +static void compaction_free(struct page *page, unsigned long data) +{ + struct compact_control *cc = (struct compact_control *)data; + + list_add(&page->lru, &cc->freepages); + cc->nr_freepages++; +} + +/* possible outcome of isolate_migratepages */ +typedef enum { + ISOLATE_ABORT, /* Abort compaction now */ + ISOLATE_NONE, /* No pages isolated, continue scanning */ + ISOLATE_SUCCESS, /* Pages isolated, migrate */ +} isolate_migrate_t; + +/* + * Allow userspace to control policy on scanning the unevictable LRU for + * compactable pages. + */ +int sysctl_compact_unevictable_allowed __read_mostly = CONFIG_COMPACT_UNEVICTABLE_DEFAULT; + +static inline void +update_fast_start_pfn(struct compact_control *cc, unsigned long pfn) +{ + if (cc->fast_start_pfn == ULONG_MAX) + return; + + if (!cc->fast_start_pfn) + cc->fast_start_pfn = pfn; + + cc->fast_start_pfn = min(cc->fast_start_pfn, pfn); +} + +static inline unsigned long +reinit_migrate_pfn(struct compact_control *cc) +{ + if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX) + return cc->migrate_pfn; + + cc->migrate_pfn = cc->fast_start_pfn; + cc->fast_start_pfn = ULONG_MAX; + + return cc->migrate_pfn; +} + +/* + * Briefly search the free lists for a migration source that already has + * some free pages to reduce the number of pages that need migration + * before a pageblock is free. + */ +static unsigned long fast_find_migrateblock(struct compact_control *cc) +{ + unsigned int limit = freelist_scan_limit(cc); + unsigned int nr_scanned = 0; + unsigned long distance; + unsigned long pfn = cc->migrate_pfn; + unsigned long high_pfn; + int order; + bool found_block = false; + + /* Skip hints are relied on to avoid repeats on the fast search */ + if (cc->ignore_skip_hint) + return pfn; + + /* + * If the migrate_pfn is not at the start of a zone or the start + * of a pageblock then assume this is a continuation of a previous + * scan restarted due to COMPACT_CLUSTER_MAX. + */ + if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn)) + return pfn; + + /* + * For smaller orders, just linearly scan as the number of pages + * to migrate should be relatively small and does not necessarily + * justify freeing up a large block for a small allocation. + */ + if (cc->order <= PAGE_ALLOC_COSTLY_ORDER) + return pfn; + + /* + * Only allow kcompactd and direct requests for movable pages to + * quickly clear out a MOVABLE pageblock for allocation. This + * reduces the risk that a large movable pageblock is freed for + * an unmovable/reclaimable small allocation. + */ + if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE) + return pfn; + + /* + * When starting the migration scanner, pick any pageblock within the + * first half of the search space. Otherwise try and pick a pageblock + * within the first eighth to reduce the chances that a migration + * target later becomes a source. + */ + distance = (cc->free_pfn - cc->migrate_pfn) >> 1; + if (cc->migrate_pfn != cc->zone->zone_start_pfn) + distance >>= 2; + high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance); + + for (order = cc->order - 1; + order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit; + order--) { + struct free_area *area = &cc->zone->free_area[order]; + struct list_head *freelist; + unsigned long flags; + struct page *freepage; + + if (!area->nr_free) + continue; + + spin_lock_irqsave(&cc->zone->lock, flags); + freelist = &area->free_list[MIGRATE_MOVABLE]; + list_for_each_entry(freepage, freelist, lru) { + unsigned long free_pfn; + + if (nr_scanned++ >= limit) { + move_freelist_tail(freelist, freepage); + break; + } + + free_pfn = page_to_pfn(freepage); + if (free_pfn < high_pfn) { + /* + * Avoid if skipped recently. Ideally it would + * move to the tail but even safe iteration of + * the list assumes an entry is deleted, not + * reordered. + */ + if (get_pageblock_skip(freepage)) + continue; + + /* Reorder to so a future search skips recent pages */ + move_freelist_tail(freelist, freepage); + + update_fast_start_pfn(cc, free_pfn); + pfn = pageblock_start_pfn(free_pfn); + if (pfn < cc->zone->zone_start_pfn) + pfn = cc->zone->zone_start_pfn; + cc->fast_search_fail = 0; + found_block = true; + set_pageblock_skip(freepage); + break; + } + } + spin_unlock_irqrestore(&cc->zone->lock, flags); + } + + cc->total_migrate_scanned += nr_scanned; + + /* + * If fast scanning failed then use a cached entry for a page block + * that had free pages as the basis for starting a linear scan. + */ + if (!found_block) { + cc->fast_search_fail++; + pfn = reinit_migrate_pfn(cc); + } + return pfn; +} + +/* + * Isolate all pages that can be migrated from the first suitable block, + * starting at the block pointed to by the migrate scanner pfn within + * compact_control. + */ +static isolate_migrate_t isolate_migratepages(struct compact_control *cc) +{ + unsigned long block_start_pfn; + unsigned long block_end_pfn; + unsigned long low_pfn; + struct page *page; + const isolate_mode_t isolate_mode = + (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) | + (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0); + bool fast_find_block; + + /* + * Start at where we last stopped, or beginning of the zone as + * initialized by compact_zone(). The first failure will use + * the lowest PFN as the starting point for linear scanning. + */ + low_pfn = fast_find_migrateblock(cc); + block_start_pfn = pageblock_start_pfn(low_pfn); + if (block_start_pfn < cc->zone->zone_start_pfn) + block_start_pfn = cc->zone->zone_start_pfn; + + /* + * fast_find_migrateblock marks a pageblock skipped so to avoid + * the isolation_suitable check below, check whether the fast + * search was successful. + */ + fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail; + + /* Only scan within a pageblock boundary */ + block_end_pfn = pageblock_end_pfn(low_pfn); + + /* + * Iterate over whole pageblocks until we find the first suitable. + * Do not cross the free scanner. + */ + for (; block_end_pfn <= cc->free_pfn; + fast_find_block = false, + cc->migrate_pfn = low_pfn = block_end_pfn, + block_start_pfn = block_end_pfn, + block_end_pfn += pageblock_nr_pages) { + + /* + * This can potentially iterate a massively long zone with + * many pageblocks unsuitable, so periodically check if we + * need to schedule. + */ + if (!(low_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages))) + cond_resched(); + + page = pageblock_pfn_to_page(block_start_pfn, + block_end_pfn, cc->zone); + if (!page) + continue; + + /* + * If isolation recently failed, do not retry. Only check the + * pageblock once. COMPACT_CLUSTER_MAX causes a pageblock + * to be visited multiple times. Assume skip was checked + * before making it "skip" so other compaction instances do + * not scan the same block. + */ + if (pageblock_aligned(low_pfn) && + !fast_find_block && !isolation_suitable(cc, page)) + continue; + + /* + * For async direct compaction, only scan the pageblocks of the + * same migratetype without huge pages. Async direct compaction + * is optimistic to see if the minimum amount of work satisfies + * the allocation. The cached PFN is updated as it's possible + * that all remaining blocks between source and target are + * unsuitable and the compaction scanners fail to meet. + */ + if (!suitable_migration_source(cc, page)) { + update_cached_migrate(cc, block_end_pfn); + continue; + } + + /* Perform the isolation */ + if (isolate_migratepages_block(cc, low_pfn, block_end_pfn, + isolate_mode)) + return ISOLATE_ABORT; + + /* + * Either we isolated something and proceed with migration. Or + * we failed and compact_zone should decide if we should + * continue or not. + */ + break; + } + + return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE; +} + +/* + * order == -1 is expected when compacting via + * /proc/sys/vm/compact_memory + */ +static inline bool is_via_compact_memory(int order) +{ + return order == -1; +} + +/* + * Determine whether kswapd is (or recently was!) running on this node. + * + * pgdat_kswapd_lock() pins pgdat->kswapd, so a concurrent kswapd_stop() can't + * zero it. + */ +static bool kswapd_is_running(pg_data_t *pgdat) +{ + bool running; + + pgdat_kswapd_lock(pgdat); + running = pgdat->kswapd && task_is_running(pgdat->kswapd); + pgdat_kswapd_unlock(pgdat); + + return running; +} + +/* + * A zone's fragmentation score is the external fragmentation wrt to the + * COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100]. + */ +static unsigned int fragmentation_score_zone(struct zone *zone) +{ + return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER); +} + +/* + * A weighted zone's fragmentation score is the external fragmentation + * wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It + * returns a value in the range [0, 100]. + * + * The scaling factor ensures that proactive compaction focuses on larger + * zones like ZONE_NORMAL, rather than smaller, specialized zones like + * ZONE_DMA32. For smaller zones, the score value remains close to zero, + * and thus never exceeds the high threshold for proactive compaction. + */ +static unsigned int fragmentation_score_zone_weighted(struct zone *zone) +{ + unsigned long score; + + score = zone->present_pages * fragmentation_score_zone(zone); + return div64_ul(score, zone->zone_pgdat->node_present_pages + 1); +} + +/* + * The per-node proactive (background) compaction process is started by its + * corresponding kcompactd thread when the node's fragmentation score + * exceeds the high threshold. The compaction process remains active till + * the node's score falls below the low threshold, or one of the back-off + * conditions is met. + */ +static unsigned int fragmentation_score_node(pg_data_t *pgdat) +{ + unsigned int score = 0; + int zoneid; + + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { + struct zone *zone; + + zone = &pgdat->node_zones[zoneid]; + score += fragmentation_score_zone_weighted(zone); + } + + return score; +} + +static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low) +{ + unsigned int wmark_low; + + /* + * Cap the low watermark to avoid excessive compaction + * activity in case a user sets the proactiveness tunable + * close to 100 (maximum). + */ + wmark_low = max(100U - sysctl_compaction_proactiveness, 5U); + return low ? wmark_low : min(wmark_low + 10, 100U); +} + +static bool should_proactive_compact_node(pg_data_t *pgdat) +{ + int wmark_high; + + if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat)) + return false; + + wmark_high = fragmentation_score_wmark(pgdat, false); + return fragmentation_score_node(pgdat) > wmark_high; +} + +static enum compact_result __compact_finished(struct compact_control *cc) +{ + unsigned int order; + const int migratetype = cc->migratetype; + int ret; + + /* Compaction run completes if the migrate and free scanner meet */ + if (compact_scanners_met(cc)) { + /* Let the next compaction start anew. */ + reset_cached_positions(cc->zone); + + /* + * Mark that the PG_migrate_skip information should be cleared + * by kswapd when it goes to sleep. kcompactd does not set the + * flag itself as the decision to be clear should be directly + * based on an allocation request. + */ + if (cc->direct_compaction) + cc->zone->compact_blockskip_flush = true; + + if (cc->whole_zone) + return COMPACT_COMPLETE; + else + return COMPACT_PARTIAL_SKIPPED; + } + + if (cc->proactive_compaction) { + int score, wmark_low; + pg_data_t *pgdat; + + pgdat = cc->zone->zone_pgdat; + if (kswapd_is_running(pgdat)) + return COMPACT_PARTIAL_SKIPPED; + + score = fragmentation_score_zone(cc->zone); + wmark_low = fragmentation_score_wmark(pgdat, true); + + if (score > wmark_low) + ret = COMPACT_CONTINUE; + else + ret = COMPACT_SUCCESS; + + goto out; + } + + if (is_via_compact_memory(cc->order)) + return COMPACT_CONTINUE; + + /* + * Always finish scanning a pageblock to reduce the possibility of + * fallbacks in the future. This is particularly important when + * migration source is unmovable/reclaimable but it's not worth + * special casing. + */ + if (!pageblock_aligned(cc->migrate_pfn)) + return COMPACT_CONTINUE; + + /* Direct compactor: Is a suitable page free? */ + ret = COMPACT_NO_SUITABLE_PAGE; + for (order = cc->order; order < MAX_ORDER; order++) { + struct free_area *area = &cc->zone->free_area[order]; + bool can_steal; + + /* Job done if page is free of the right migratetype */ + if (!free_area_empty(area, migratetype)) + return COMPACT_SUCCESS; + +#ifdef CONFIG_CMA + /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */ + if (migratetype == MIGRATE_MOVABLE && + !free_area_empty(area, MIGRATE_CMA)) + return COMPACT_SUCCESS; +#endif + /* + * Job done if allocation would steal freepages from + * other migratetype buddy lists. + */ + if (find_suitable_fallback(area, order, migratetype, + true, &can_steal) != -1) + /* + * Movable pages are OK in any pageblock. If we are + * stealing for a non-movable allocation, make sure + * we finish compacting the current pageblock first + * (which is assured by the above migrate_pfn align + * check) so it is as free as possible and we won't + * have to steal another one soon. + */ + return COMPACT_SUCCESS; + } + +out: + if (cc->contended || fatal_signal_pending(current)) + ret = COMPACT_CONTENDED; + + return ret; +} + +static enum compact_result compact_finished(struct compact_control *cc) +{ + int ret; + + ret = __compact_finished(cc); + trace_mm_compaction_finished(cc->zone, cc->order, ret); + if (ret == COMPACT_NO_SUITABLE_PAGE) + ret = COMPACT_CONTINUE; + + return ret; +} + +static enum compact_result __compaction_suitable(struct zone *zone, int order, + unsigned int alloc_flags, + int highest_zoneidx, + unsigned long wmark_target) +{ + unsigned long watermark; + + if (is_via_compact_memory(order)) + return COMPACT_CONTINUE; + + watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK); + /* + * If watermarks for high-order allocation are already met, there + * should be no need for compaction at all. + */ + if (zone_watermark_ok(zone, order, watermark, highest_zoneidx, + alloc_flags)) + return COMPACT_SUCCESS; + + /* + * Watermarks for order-0 must be met for compaction to be able to + * isolate free pages for migration targets. This means that the + * watermark and alloc_flags have to match, or be more pessimistic than + * the check in __isolate_free_page(). We don't use the direct + * compactor's alloc_flags, as they are not relevant for freepage + * isolation. We however do use the direct compactor's highest_zoneidx + * to skip over zones where lowmem reserves would prevent allocation + * even if compaction succeeds. + * For costly orders, we require low watermark instead of min for + * compaction to proceed to increase its chances. + * ALLOC_CMA is used, as pages in CMA pageblocks are considered + * suitable migration targets + */ + watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ? + low_wmark_pages(zone) : min_wmark_pages(zone); + watermark += compact_gap(order); + if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx, + ALLOC_CMA, wmark_target)) + return COMPACT_SKIPPED; + + return COMPACT_CONTINUE; +} + +/* + * compaction_suitable: Is this suitable to run compaction on this zone now? + * Returns + * COMPACT_SKIPPED - If there are too few free pages for compaction + * COMPACT_SUCCESS - If the allocation would succeed without compaction + * COMPACT_CONTINUE - If compaction should run now + */ +enum compact_result compaction_suitable(struct zone *zone, int order, + unsigned int alloc_flags, + int highest_zoneidx) +{ + enum compact_result ret; + int fragindex; + + ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx, + zone_page_state(zone, NR_FREE_PAGES)); + /* + * fragmentation index determines if allocation failures are due to + * low memory or external fragmentation + * + * index of -1000 would imply allocations might succeed depending on + * watermarks, but we already failed the high-order watermark check + * index towards 0 implies failure is due to lack of memory + * index towards 1000 implies failure is due to fragmentation + * + * Only compact if a failure would be due to fragmentation. Also + * ignore fragindex for non-costly orders where the alternative to + * a successful reclaim/compaction is OOM. Fragindex and the + * vm.extfrag_threshold sysctl is meant as a heuristic to prevent + * excessive compaction for costly orders, but it should not be at the + * expense of system stability. + */ + if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) { + fragindex = fragmentation_index(zone, order); + if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold) + ret = COMPACT_NOT_SUITABLE_ZONE; + } + + trace_mm_compaction_suitable(zone, order, ret); + if (ret == COMPACT_NOT_SUITABLE_ZONE) + ret = COMPACT_SKIPPED; + + return ret; +} + +bool compaction_zonelist_suitable(struct alloc_context *ac, int order, + int alloc_flags) +{ + struct zone *zone; + struct zoneref *z; + + /* + * Make sure at least one zone would pass __compaction_suitable if we continue + * retrying the reclaim. + */ + for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, + ac->highest_zoneidx, ac->nodemask) { + unsigned long available; + enum compact_result compact_result; + + /* + * Do not consider all the reclaimable memory because we do not + * want to trash just for a single high order allocation which + * is even not guaranteed to appear even if __compaction_suitable + * is happy about the watermark check. + */ + available = zone_reclaimable_pages(zone) / order; + available += zone_page_state_snapshot(zone, NR_FREE_PAGES); + compact_result = __compaction_suitable(zone, order, alloc_flags, + ac->highest_zoneidx, available); + if (compact_result == COMPACT_CONTINUE) + return true; + } + + return false; +} + +static enum compact_result +compact_zone(struct compact_control *cc, struct capture_control *capc) +{ + enum compact_result ret; + unsigned long start_pfn = cc->zone->zone_start_pfn; + unsigned long end_pfn = zone_end_pfn(cc->zone); + unsigned long last_migrated_pfn; + const bool sync = cc->mode != MIGRATE_ASYNC; + bool update_cached; + unsigned int nr_succeeded = 0; + + /* + * These counters track activities during zone compaction. Initialize + * them before compacting a new zone. + */ + cc->total_migrate_scanned = 0; + cc->total_free_scanned = 0; + cc->nr_migratepages = 0; + cc->nr_freepages = 0; + INIT_LIST_HEAD(&cc->freepages); + INIT_LIST_HEAD(&cc->migratepages); + + cc->migratetype = gfp_migratetype(cc->gfp_mask); + ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags, + cc->highest_zoneidx); + /* Compaction is likely to fail */ + if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED) + return ret; + + /* huh, compaction_suitable is returning something unexpected */ + VM_BUG_ON(ret != COMPACT_CONTINUE); + + /* + * Clear pageblock skip if there were failures recently and compaction + * is about to be retried after being deferred. + */ + if (compaction_restarting(cc->zone, cc->order)) + __reset_isolation_suitable(cc->zone); + + /* + * Setup to move all movable pages to the end of the zone. Used cached + * information on where the scanners should start (unless we explicitly + * want to compact the whole zone), but check that it is initialised + * by ensuring the values are within zone boundaries. + */ + cc->fast_start_pfn = 0; + if (cc->whole_zone) { + cc->migrate_pfn = start_pfn; + cc->free_pfn = pageblock_start_pfn(end_pfn - 1); + } else { + cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync]; + cc->free_pfn = cc->zone->compact_cached_free_pfn; + if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) { + cc->free_pfn = pageblock_start_pfn(end_pfn - 1); + cc->zone->compact_cached_free_pfn = cc->free_pfn; + } + if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) { + cc->migrate_pfn = start_pfn; + cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn; + cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn; + } + + if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn) + cc->whole_zone = true; + } + + last_migrated_pfn = 0; + + /* + * Migrate has separate cached PFNs for ASYNC and SYNC* migration on + * the basis that some migrations will fail in ASYNC mode. However, + * if the cached PFNs match and pageblocks are skipped due to having + * no isolation candidates, then the sync state does not matter. + * Until a pageblock with isolation candidates is found, keep the + * cached PFNs in sync to avoid revisiting the same blocks. + */ + update_cached = !sync && + cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1]; + + trace_mm_compaction_begin(cc, start_pfn, end_pfn, sync); + + /* lru_add_drain_all could be expensive with involving other CPUs */ + lru_add_drain(); + + while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) { + int err; + unsigned long iteration_start_pfn = cc->migrate_pfn; + + /* + * Avoid multiple rescans which can happen if a page cannot be + * isolated (dirty/writeback in async mode) or if the migrated + * pages are being allocated before the pageblock is cleared. + * The first rescan will capture the entire pageblock for + * migration. If it fails, it'll be marked skip and scanning + * will proceed as normal. + */ + cc->rescan = false; + if (pageblock_start_pfn(last_migrated_pfn) == + pageblock_start_pfn(iteration_start_pfn)) { + cc->rescan = true; + } + + switch (isolate_migratepages(cc)) { + case ISOLATE_ABORT: + ret = COMPACT_CONTENDED; + putback_movable_pages(&cc->migratepages); + cc->nr_migratepages = 0; + goto out; + case ISOLATE_NONE: + if (update_cached) { + cc->zone->compact_cached_migrate_pfn[1] = + cc->zone->compact_cached_migrate_pfn[0]; + } + + /* + * We haven't isolated and migrated anything, but + * there might still be unflushed migrations from + * previous cc->order aligned block. + */ + goto check_drain; + case ISOLATE_SUCCESS: + update_cached = false; + last_migrated_pfn = iteration_start_pfn; + } + + err = migrate_pages(&cc->migratepages, compaction_alloc, + compaction_free, (unsigned long)cc, cc->mode, + MR_COMPACTION, &nr_succeeded); + + trace_mm_compaction_migratepages(cc, nr_succeeded); + + /* All pages were either migrated or will be released */ + cc->nr_migratepages = 0; + if (err) { + putback_movable_pages(&cc->migratepages); + /* + * migrate_pages() may return -ENOMEM when scanners meet + * and we want compact_finished() to detect it + */ + if (err == -ENOMEM && !compact_scanners_met(cc)) { + ret = COMPACT_CONTENDED; + goto out; + } + /* + * We failed to migrate at least one page in the current + * order-aligned block, so skip the rest of it. + */ + if (cc->direct_compaction && + (cc->mode == MIGRATE_ASYNC)) { + cc->migrate_pfn = block_end_pfn( + cc->migrate_pfn - 1, cc->order); + /* Draining pcplists is useless in this case */ + last_migrated_pfn = 0; + } + } + +check_drain: + /* + * Has the migration scanner moved away from the previous + * cc->order aligned block where we migrated from? If yes, + * flush the pages that were freed, so that they can merge and + * compact_finished() can detect immediately if allocation + * would succeed. + */ + if (cc->order > 0 && last_migrated_pfn) { + unsigned long current_block_start = + block_start_pfn(cc->migrate_pfn, cc->order); + + if (last_migrated_pfn < current_block_start) { + lru_add_drain_cpu_zone(cc->zone); + /* No more flushing until we migrate again */ + last_migrated_pfn = 0; + } + } + + /* Stop if a page has been captured */ + if (capc && capc->page) { + ret = COMPACT_SUCCESS; + break; + } + } + +out: + /* + * Release free pages and update where the free scanner should restart, + * so we don't leave any returned pages behind in the next attempt. + */ + if (cc->nr_freepages > 0) { + unsigned long free_pfn = release_freepages(&cc->freepages); + + cc->nr_freepages = 0; + VM_BUG_ON(free_pfn == 0); + /* The cached pfn is always the first in a pageblock */ + free_pfn = pageblock_start_pfn(free_pfn); + /* + * Only go back, not forward. The cached pfn might have been + * already reset to zone end in compact_finished() + */ + if (free_pfn > cc->zone->compact_cached_free_pfn) + cc->zone->compact_cached_free_pfn = free_pfn; + } + + count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned); + count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned); + + trace_mm_compaction_end(cc, start_pfn, end_pfn, sync, ret); + + return ret; +} + +static enum compact_result compact_zone_order(struct zone *zone, int order, + gfp_t gfp_mask, enum compact_priority prio, + unsigned int alloc_flags, int highest_zoneidx, + struct page **capture) +{ + enum compact_result ret; + struct compact_control cc = { + .order = order, + .search_order = order, + .gfp_mask = gfp_mask, + .zone = zone, + .mode = (prio == COMPACT_PRIO_ASYNC) ? + MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT, + .alloc_flags = alloc_flags, + .highest_zoneidx = highest_zoneidx, + .direct_compaction = true, + .whole_zone = (prio == MIN_COMPACT_PRIORITY), + .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY), + .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY) + }; + struct capture_control capc = { + .cc = &cc, + .page = NULL, + }; + + /* + * Make sure the structs are really initialized before we expose the + * capture control, in case we are interrupted and the interrupt handler + * frees a page. + */ + barrier(); + WRITE_ONCE(current->capture_control, &capc); + + ret = compact_zone(&cc, &capc); + + VM_BUG_ON(!list_empty(&cc.freepages)); + VM_BUG_ON(!list_empty(&cc.migratepages)); + + /* + * Make sure we hide capture control first before we read the captured + * page pointer, otherwise an interrupt could free and capture a page + * and we would leak it. + */ + WRITE_ONCE(current->capture_control, NULL); + *capture = READ_ONCE(capc.page); + /* + * Technically, it is also possible that compaction is skipped but + * the page is still captured out of luck(IRQ came and freed the page). + * Returning COMPACT_SUCCESS in such cases helps in properly accounting + * the COMPACT[STALL|FAIL] when compaction is skipped. + */ + if (*capture) + ret = COMPACT_SUCCESS; + + return ret; +} + +int sysctl_extfrag_threshold = 500; + +/** + * try_to_compact_pages - Direct compact to satisfy a high-order allocation + * @gfp_mask: The GFP mask of the current allocation + * @order: The order of the current allocation + * @alloc_flags: The allocation flags of the current allocation + * @ac: The context of current allocation + * @prio: Determines how hard direct compaction should try to succeed + * @capture: Pointer to free page created by compaction will be stored here + * + * This is the main entry point for direct page compaction. + */ +enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order, + unsigned int alloc_flags, const struct alloc_context *ac, + enum compact_priority prio, struct page **capture) +{ + int may_perform_io = (__force int)(gfp_mask & __GFP_IO); + struct zoneref *z; + struct zone *zone; + enum compact_result rc = COMPACT_SKIPPED; + + /* + * Check if the GFP flags allow compaction - GFP_NOIO is really + * tricky context because the migration might require IO + */ + if (!may_perform_io) + return COMPACT_SKIPPED; + + trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio); + + /* Compact each zone in the list */ + for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, + ac->highest_zoneidx, ac->nodemask) { + enum compact_result status; + + if (prio > MIN_COMPACT_PRIORITY + && compaction_deferred(zone, order)) { + rc = max_t(enum compact_result, COMPACT_DEFERRED, rc); + continue; + } + + status = compact_zone_order(zone, order, gfp_mask, prio, + alloc_flags, ac->highest_zoneidx, capture); + rc = max(status, rc); + + /* The allocation should succeed, stop compacting */ + if (status == COMPACT_SUCCESS) { + /* + * We think the allocation will succeed in this zone, + * but it is not certain, hence the false. The caller + * will repeat this with true if allocation indeed + * succeeds in this zone. + */ + compaction_defer_reset(zone, order, false); + + break; + } + + if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE || + status == COMPACT_PARTIAL_SKIPPED)) + /* + * We think that allocation won't succeed in this zone + * so we defer compaction there. If it ends up + * succeeding after all, it will be reset. + */ + defer_compaction(zone, order); + + /* + * We might have stopped compacting due to need_resched() in + * async compaction, or due to a fatal signal detected. In that + * case do not try further zones + */ + if ((prio == COMPACT_PRIO_ASYNC && need_resched()) + || fatal_signal_pending(current)) + break; + } + + return rc; +} + +/* + * Compact all zones within a node till each zone's fragmentation score + * reaches within proactive compaction thresholds (as determined by the + * proactiveness tunable). + * + * It is possible that the function returns before reaching score targets + * due to various back-off conditions, such as, contention on per-node or + * per-zone locks. + */ +static void proactive_compact_node(pg_data_t *pgdat) +{ + int zoneid; + struct zone *zone; + struct compact_control cc = { + .order = -1, + .mode = MIGRATE_SYNC_LIGHT, + .ignore_skip_hint = true, + .whole_zone = true, + .gfp_mask = GFP_KERNEL, + .proactive_compaction = true, + }; + + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { + zone = &pgdat->node_zones[zoneid]; + if (!populated_zone(zone)) + continue; + + cc.zone = zone; + + compact_zone(&cc, NULL); + + VM_BUG_ON(!list_empty(&cc.freepages)); + VM_BUG_ON(!list_empty(&cc.migratepages)); + } +} + +/* Compact all zones within a node */ +static void compact_node(int nid) +{ + pg_data_t *pgdat = NODE_DATA(nid); + int zoneid; + struct zone *zone; + struct compact_control cc = { + .order = -1, + .mode = MIGRATE_SYNC, + .ignore_skip_hint = true, + .whole_zone = true, + .gfp_mask = GFP_KERNEL, + }; + + + for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) { + + zone = &pgdat->node_zones[zoneid]; + if (!populated_zone(zone)) + continue; + + cc.zone = zone; + + compact_zone(&cc, NULL); + + VM_BUG_ON(!list_empty(&cc.freepages)); + VM_BUG_ON(!list_empty(&cc.migratepages)); + } +} + +/* Compact all nodes in the system */ +static void compact_nodes(void) +{ + int nid; + + /* Flush pending updates to the LRU lists */ + lru_add_drain_all(); + + for_each_online_node(nid) + compact_node(nid); +} + +/* + * Tunable for proactive compaction. It determines how + * aggressively the kernel should compact memory in the + * background. It takes values in the range [0, 100]. + */ +unsigned int __read_mostly sysctl_compaction_proactiveness = 20; + +int compaction_proactiveness_sysctl_handler(struct ctl_table *table, int write, + void *buffer, size_t *length, loff_t *ppos) +{ + int rc, nid; + + rc = proc_dointvec_minmax(table, write, buffer, length, ppos); + if (rc) + return rc; + + if (write && sysctl_compaction_proactiveness) { + for_each_online_node(nid) { + pg_data_t *pgdat = NODE_DATA(nid); + + if (pgdat->proactive_compact_trigger) + continue; + + pgdat->proactive_compact_trigger = true; + wake_up_interruptible(&pgdat->kcompactd_wait); + } + } + + return 0; +} + +/* + * This is the entry point for compacting all nodes via + * /proc/sys/vm/compact_memory + */ +int sysctl_compaction_handler(struct ctl_table *table, int write, + void *buffer, size_t *length, loff_t *ppos) +{ + if (write) + compact_nodes(); + + return 0; +} + +#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA) +static ssize_t compact_store(struct device *dev, + struct device_attribute *attr, + const char *buf, size_t count) +{ + int nid = dev->id; + + if (nid >= 0 && nid < nr_node_ids && node_online(nid)) { + /* Flush pending updates to the LRU lists */ + lru_add_drain_all(); + + compact_node(nid); + } + + return count; +} +static DEVICE_ATTR_WO(compact); + +int compaction_register_node(struct node *node) +{ + return device_create_file(&node->dev, &dev_attr_compact); +} + +void compaction_unregister_node(struct node *node) +{ + return device_remove_file(&node->dev, &dev_attr_compact); +} +#endif /* CONFIG_SYSFS && CONFIG_NUMA */ + +static inline bool kcompactd_work_requested(pg_data_t *pgdat) +{ + return pgdat->kcompactd_max_order > 0 || kthread_should_stop() || + pgdat->proactive_compact_trigger; +} + +static bool kcompactd_node_suitable(pg_data_t *pgdat) +{ + int zoneid; + struct zone *zone; + enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx; + + for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) { + zone = &pgdat->node_zones[zoneid]; + + if (!populated_zone(zone)) + continue; + + if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0, + highest_zoneidx) == COMPACT_CONTINUE) + return true; + } + + return false; +} + +static void kcompactd_do_work(pg_data_t *pgdat) +{ + /* + * With no special task, compact all zones so that a page of requested + * order is allocatable. + */ + int zoneid; + struct zone *zone; + struct compact_control cc = { + .order = pgdat->kcompactd_max_order, + .search_order = pgdat->kcompactd_max_order, + .highest_zoneidx = pgdat->kcompactd_highest_zoneidx, + .mode = MIGRATE_SYNC_LIGHT, + .ignore_skip_hint = false, + .gfp_mask = GFP_KERNEL, + }; + trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order, + cc.highest_zoneidx); + count_compact_event(KCOMPACTD_WAKE); + + for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) { + int status; + + zone = &pgdat->node_zones[zoneid]; + if (!populated_zone(zone)) + continue; + + if (compaction_deferred(zone, cc.order)) + continue; + + if (compaction_suitable(zone, cc.order, 0, zoneid) != + COMPACT_CONTINUE) + continue; + + if (kthread_should_stop()) + return; + + cc.zone = zone; + status = compact_zone(&cc, NULL); + + if (status == COMPACT_SUCCESS) { + compaction_defer_reset(zone, cc.order, false); + } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) { + /* + * Buddy pages may become stranded on pcps that could + * otherwise coalesce on the zone's free area for + * order >= cc.order. This is ratelimited by the + * upcoming deferral. + */ + drain_all_pages(zone); + + /* + * We use sync migration mode here, so we defer like + * sync direct compaction does. + */ + defer_compaction(zone, cc.order); + } + + count_compact_events(KCOMPACTD_MIGRATE_SCANNED, + cc.total_migrate_scanned); + count_compact_events(KCOMPACTD_FREE_SCANNED, + cc.total_free_scanned); + + VM_BUG_ON(!list_empty(&cc.freepages)); + VM_BUG_ON(!list_empty(&cc.migratepages)); + } + + /* + * Regardless of success, we are done until woken up next. But remember + * the requested order/highest_zoneidx in case it was higher/tighter + * than our current ones + */ + if (pgdat->kcompactd_max_order <= cc.order) + pgdat->kcompactd_max_order = 0; + if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx) + pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1; +} + +void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx) +{ + if (!order) + return; + + if (pgdat->kcompactd_max_order < order) + pgdat->kcompactd_max_order = order; + + if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx) + pgdat->kcompactd_highest_zoneidx = highest_zoneidx; + + /* + * Pairs with implicit barrier in wait_event_freezable() + * such that wakeups are not missed. + */ + if (!wq_has_sleeper(&pgdat->kcompactd_wait)) + return; + + if (!kcompactd_node_suitable(pgdat)) + return; + + trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order, + highest_zoneidx); + wake_up_interruptible(&pgdat->kcompactd_wait); +} + +/* + * The background compaction daemon, started as a kernel thread + * from the init process. + */ +static int kcompactd(void *p) +{ + pg_data_t *pgdat = (pg_data_t *)p; + struct task_struct *tsk = current; + long default_timeout = msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC); + long timeout = default_timeout; + + const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); + + if (!cpumask_empty(cpumask)) + set_cpus_allowed_ptr(tsk, cpumask); + + set_freezable(); + + pgdat->kcompactd_max_order = 0; + pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1; + + while (!kthread_should_stop()) { + unsigned long pflags; + + /* + * Avoid the unnecessary wakeup for proactive compaction + * when it is disabled. + */ + if (!sysctl_compaction_proactiveness) + timeout = MAX_SCHEDULE_TIMEOUT; + trace_mm_compaction_kcompactd_sleep(pgdat->node_id); + if (wait_event_freezable_timeout(pgdat->kcompactd_wait, + kcompactd_work_requested(pgdat), timeout) && + !pgdat->proactive_compact_trigger) { + + psi_memstall_enter(&pflags); + kcompactd_do_work(pgdat); + psi_memstall_leave(&pflags); + /* + * Reset the timeout value. The defer timeout from + * proactive compaction is lost here but that is fine + * as the condition of the zone changing substantionally + * then carrying on with the previous defer interval is + * not useful. + */ + timeout = default_timeout; + continue; + } + + /* + * Start the proactive work with default timeout. Based + * on the fragmentation score, this timeout is updated. + */ + timeout = default_timeout; + if (should_proactive_compact_node(pgdat)) { + unsigned int prev_score, score; + + prev_score = fragmentation_score_node(pgdat); + proactive_compact_node(pgdat); + score = fragmentation_score_node(pgdat); + /* + * Defer proactive compaction if the fragmentation + * score did not go down i.e. no progress made. + */ + if (unlikely(score >= prev_score)) + timeout = + default_timeout << COMPACT_MAX_DEFER_SHIFT; + } + if (unlikely(pgdat->proactive_compact_trigger)) + pgdat->proactive_compact_trigger = false; + } + + return 0; +} + +/* + * This kcompactd start function will be called by init and node-hot-add. + * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added. + */ +void kcompactd_run(int nid) +{ + pg_data_t *pgdat = NODE_DATA(nid); + + if (pgdat->kcompactd) + return; + + pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid); + if (IS_ERR(pgdat->kcompactd)) { + pr_err("Failed to start kcompactd on node %d\n", nid); + pgdat->kcompactd = NULL; + } +} + +/* + * Called by memory hotplug when all memory in a node is offlined. Caller must + * be holding mem_hotplug_begin/done(). + */ +void kcompactd_stop(int nid) +{ + struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd; + + if (kcompactd) { + kthread_stop(kcompactd); + NODE_DATA(nid)->kcompactd = NULL; + } +} + +/* + * It's optimal to keep kcompactd on the same CPUs as their memory, but + * not required for correctness. So if the last cpu in a node goes + * away, we get changed to run anywhere: as the first one comes back, + * restore their cpu bindings. + */ +static int kcompactd_cpu_online(unsigned int cpu) +{ + int nid; + + for_each_node_state(nid, N_MEMORY) { + pg_data_t *pgdat = NODE_DATA(nid); + const struct cpumask *mask; + + mask = cpumask_of_node(pgdat->node_id); + + if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) + /* One of our CPUs online: restore mask */ + if (pgdat->kcompactd) + set_cpus_allowed_ptr(pgdat->kcompactd, mask); + } + return 0; +} + +static int __init kcompactd_init(void) +{ + int nid; + int ret; + + ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, + "mm/compaction:online", + kcompactd_cpu_online, NULL); + if (ret < 0) { + pr_err("kcompactd: failed to register hotplug callbacks.\n"); + return ret; + } + + for_each_node_state(nid, N_MEMORY) + kcompactd_run(nid); + return 0; +} +subsys_initcall(kcompactd_init) + +#endif /* CONFIG_COMPACTION */ |